I take all your points, but:
Topping and leaving, which is the norm, results in a very different form to topping and formative pruning. The only place I have ever seen (and done) the latter is in fruit trees, which are usually artificially maintained at a lower height than they would naturally form, and have on occasion been literally topped, to bring them down to a different height to change the picking method. With appropriate management, the head can be re-formed to a natural appearance, granted at a cost and requiring a good eye. I also fully accept that this is not normal practice in arboriculture, but P.cerasifera responds in similar fashion to P.domestica so there is no reason it couldn't be done that I can see, however unconventional it may be.
I had a quick look at P.cerasifera Nigra on Barchams. They supply at £164 inc. VAT for medium (3-4m). These would then need double staking and ties. It depends on where you needed delivery to, but this would add between £50 and £150 in their local region. All-in, the costs for trees, sundries and delivery could be pushing £500. Add the costs of felling, removal and grinding, together with the cost of planting and I would guess you are pushing £800-£1000 all in.
It would be great if the builder felt that they were liable for this, but if they don't I'm not sure there is much you could do about it. There is unlikely to be a written specification and, although it is clearly not compliant with best practice or any BS, they have clearly 'pruned the trees' so it could be a long, hard road to get any financial recompense and I wouldn't want to count on it, particularly a figure in line with the above which is likely to lie well above a goodwill gesture.
As such, whilst I agree that the OP should not have to 'make do', sadly they may have to.
With regard to the silverleaf question - yes it's a risk, but not as high as you may fear. Silverleaf is fungal and causes silvering of the leaves as its most visible sign. Severe stress can result in a physiological condition known as 'false silver leaf' which has the same visible effect. To check which, cut off an apparently infected but sacrificial branch and if it has a purple stain up the middle it's silverleaf or (much easier in your case) wait and see if the affected branches die or the tree recovers.
Alec